diff options
Diffstat (limited to 'audio/softsynth/mt32/LA32FloatWaveGenerator.cpp')
| -rw-r--r-- | audio/softsynth/mt32/LA32FloatWaveGenerator.cpp | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/audio/softsynth/mt32/LA32FloatWaveGenerator.cpp b/audio/softsynth/mt32/LA32FloatWaveGenerator.cpp index 486942b75c..0c9687b4d8 100644 --- a/audio/softsynth/mt32/LA32FloatWaveGenerator.cpp +++ b/audio/softsynth/mt32/LA32FloatWaveGenerator.cpp @@ -315,15 +315,29 @@ void LA32PartialPair::generateNextSample(const PairType useMaster, const Bit32u } } +static inline float produceDistortedSample(float sample) { + if (sample < -1.0f) { + return sample + 2.0f; + } else if (1.0f < sample) { + return sample - 2.0f; + } + return sample; +} + float LA32PartialPair::nextOutSample() { - float outputSample; - if (ringModulated) { - float ringModulatedSample = masterOutputSample * slaveOutputSample; - outputSample = mixed ? masterOutputSample + ringModulatedSample : ringModulatedSample; - } else { - outputSample = masterOutputSample + slaveOutputSample; + if (!ringModulated) { + return masterOutputSample + slaveOutputSample; } - return outputSample; + /* + * SEMI-CONFIRMED: Ring modulation model derived from sample analysis of specially constructed patches which exploit distortion. + * LA32 ring modulator found to produce distorted output in case if the absolute value of maximal amplitude of one of the input partials exceeds 8191. + * This is easy to reproduce using synth partials with resonance values close to the maximum. It looks like an integer overflow happens in this case. + * As the distortion is strictly bound to the amplitude of the complete mixed square + resonance wave in the linear space, + * it is reasonable to assume the ring modulation is performed also in the linear space by sample multiplication. + * Most probably the overflow is caused by limited precision of the multiplication circuit as the very similar distortion occurs with panning. + */ + float ringModulatedSample = produceDistortedSample(masterOutputSample) * produceDistortedSample(slaveOutputSample); + return mixed ? masterOutputSample + ringModulatedSample : ringModulatedSample; } void LA32PartialPair::deactivate(const PairType useMaster) { |